The present invention relates to a method for introducing reeled tubing into oil and gas earth wells and, more particularly, to such a method which reduces damage to the wells and prevents jamming of the reeled tubing in the wells.
In the operation of subterranean oil and gas earth wells, relatively small-diameter, thin-walled, continuous-length reeled, or coiled, tubing is now being used in certain applications in place of wireline or the like, since reeled tubing has several advantages. For example, reeled tubing does not rely on gravity for setting and retrieving the operating tools can thus can traverse highly deviated, or horizontal, earth wells. Also, reeled tubing can be more rapidly inserted into the well and can be more easily passed through downhole equipment. Also, fluids such as water, foam, paraffin, corrosion inhibitors, spotting acid, cement, and the like, can be conveyed by the reeled tubing to the well for performing various functions including washing and cleaning. Further, when used with operating tools the reeled tubing can be used to convey fluids to the operating tool to hydraulically actuate the tool.
Reeled tubing is usually made from soft-sheet steel which is rolled and induction welded along its length before being spooled onto a deployment reel. The tubing is then heat-treated on the reel to stress-relieve the tubing wall and the seam weld. Several sections of tubing are then butt-welded together to achieve lengths of up to several thousand feet for reaching the treatment zone in the well.
In the deployment of reeled tubing, the tubing is unreeled from the reel, typically at or near ground level and usually passed over a goose-neck and into an injector head located axially above the wellhead and the wellbore. The injector head typically comprises a dual chain-driven mechanism which drives the reeled tubing into, and pulls the tubing from, the well.
During this process, torsional forces are applied to the tubing as it is wound on, and unwound from the reel and passed upwardly to the goose-neck. Also, the tubing is plastically deformed as it is drawn from the reel and passed over the goose-neck and into the injector head. Further, tensil forces are applied to the tubing due to the pulling force of the injector head drive mechanism and a braking or rewind force applied at the reel. Also, the tubing leaving the injector head and going into the well is disposed in the well in a long helix which causes the tubing and especially the end thereof, to engage the walls of the well which often causes damage to casing well tubing, or the like, disposed in the well.
This problem is compounded since, once the zone of treatment has been reached by the end of the reeled tubing, typical operations may require cycling of the reeled tubing upwardly and downwardly over an interval up of hundreds of feet causing bending and unbending of portions of the reeled tubing located at or near the surface as the tubing passes and re-passes the injector head, the goose-neck and the reel. Finally, in removing the reeled tubing from the well, the entire length of the deployed tubing is again subjected to all of the above forces and plastic bending in reverse order as it is wound back onto its reel, further increasing the changes of damage to the casing and/or well tubing. Also as a result of all of the foregoing, the end portion of the reeled tends to lodge, or jam, in the well, especially in wells having a horizontal portion.